The present invention relates to bacteria strains which produce lactate and to L. johnsonii strains and further to recombinant, i.e., genetically modified/bacteria strains.
Fermentation is a degradation of a carbon source during which the final hydrogen acceptor is an organic compound. By way of lactic acid fermentation, certain bacterial strains produce a racemic mixture of the two isomeric forms of lactate, D(-)-lactate and L(+)-lactate, for the regeneration of NAD.sup.+, by the reduction of pyruvate by means of two specific NAD-dependent lactate dehydrogenases.
Some individuals are known to exhibit an intolerance to the reduction of lactose. This poor digestion of lactose is often due to the absence of a sufficient amount of .beta.-galactosidase in the small intestine. Various studies (Kolars et al., N. Engl. J. Med., 310, 1-3, 1984; Marteau et al., Br. J. Nutr., 64, 71-79, 1990; and Arrigoni et al., Am. J. Clin. Nutr., 60, 926-929, 1994) have demonstrated the fact that these people digest and tolerate the lactose contained in yoghurts better than that contained in milk. This better digestion and better lactose tolerance are due especially to the activity of the .beta.-galactosidase of the bacteria contained in yoghurts during intestinal transit.
It is further known that D(-)-lactate can give rise to acidosis problems in children. For these reasons, the World Health Organization (FAO/WHO, 1967; 1974) recommends that D(-)-lactate should not be added to children's food, either on its own or as a racemic mixture with L(+)-lactate. Also, the daily consumption limit of D(-)-lactate for adults preferably does not exceed 100 mg/kg of the human body.
Bacterial strains which have been genetically recombined so as to produce only L(+)-lactate are now known.
T. Bhowmik et al. (Appl. Microbiol. Biotechnol., 432-439, 1994) describe a technique for the isolation and inactivation, by directed mutagenesis, of the gene coding for the enzyme D-lactate dehydrogenase of the strain Lactobacillus helveticus CNRZ32, particularly the strain Lactobacillus helveticus CNRZ32(pSUW104), which produces only L(+)-lactate. This strain is obtained by the electroporation of integrating vector pSUW104, which comprises vector pSA3 and the 0.6 kb SalI-SphI internal fragment of the gene coding for the enzyme D-lactate dehydrogenase of Lactobacillus helveticus.
However, bacterial strains with the capacity to survive in the intestine, adhere to intestinal cells and effect immunomodulation, which have been genetically recombined so as to produce only L(+)-lactate, are not known at the present time. Now, it would be very valuable, for the preparation of food products, to have such bacterial strains with the capacity to survive in the intestinal tract, which possess these beneficial properties on human health and produce only L(+)-lactate, so as to avoid the adverse effects due to D(-)-lactate.
The object of the present invention is to meet these needs.